1. Field of the Invention
The present invention generally relates to electrophotographic scanners and, more particularly, to those adapted to use an external light source to illuminate an object to be scanned. For the purposes of this patent disclosure, the term “external light source” can be taken to mean a light source from a device other than the scanner itself, e.g., a cathode ray tube (“CRT”) of a computer (“CPU”) monitor.
As use of personal computers and their peripheral equipment has proliferated, the available space on user desktops has become extremely crowded and, hence, valuable. The term “footprint” has, in part, arisen out of concerns for conserving desktop space. Computer and peripheral equipment manufacturers have used various approaches in addressing the desktop crowding problem. These approaches have included various stacking schemes (such as stacking a monitor or printer on top of a computer's chassis), combining a mouse and a keyboard in an integral unit, providing scanners with sheet feed devices and by simply making computers and peripherals narrower and taller.
2. Description of Related Art re: Scanner Footprint Concerns
Manufacturers of scanners also have made some strides in reducing the footprints of their products. For example, scanners having automated feed mechanisms generally take up less overall desktop space than hand-fed scanners. Unfortunately, scanners having automatic feeding devices similar to those used to feed sheets of paper from a stack are not well suited to scanning photos, other fragile documents or objects considerably thicker than a sheet of paper. This unsuitability follows from the fact that photos, fragile documents and documents thicker than a sheet of paper can not be bent to the degree that a sheet of paper is bent in those scanners devoted to scanning sheets of paper that are automatically fed from a stack. Such bending would seriously damage photos or other fragile or thick documents. These circumstances have forced many scanner users to purchase, and dedicate valuable desktop space to, flatbed desktop scanners.
Scanner footprint concerns also have been addressed, in a somewhat indirect manner, by improving the portability of certain desktop scanners—namely so-called “portable” scanners. Portable scanners have been specifically designed to be highly compact in construction and very light in weight. A great deal of the cost, size and weight reductions associated with portable scanners has been achieved by limiting the number of “onboard” components required to operate them. For example, U.S. Pat. No. 5,680,375 teaches a portable scanner that employs a light source (e.g., the CRT of a video monitor unit associated with a computer), power sources, processors and data storage capabilities that are entirely external to that portable scanner. In short, portable scanner designers have sought to use whatever equipment is available in a desktop working environment. It should be understood, however, that even though many portable scanners have attached their scanner screens to the face of a computer monitor, the remainder of such portable scanners still takes up valuable desktop space. It would, therefore, be desirable to have a low cost scanner with the functionality of a flatbed scanner—without taking up the desktop space that self-contained scanners, or portable scanners, normally require.
3. Description of Related Art re: Scanning Technology
Scanning devices image an object by sequentially focusing arrays of light beams on narrow portions of that object. A portion of light reflected from the object is focused on a linear array of photosensors. A line portion of the object imaged on such a photosensor array is often referred to as a “scan line”. As the light source is moved relative to the object, a plurality of scan line images is formed. In effect, this plurality of images “becomes” the object.
A portion of the linear array of photosensors corresponds to a small area on a scan line. These small areas are often referred to as “picture elements” or “pixels”. The photodetectors associated with these small areas of a scan line also are often called “pixels”. Be that as it may, each photodetector in such an array will respond to the light intensity produced by a pixel location on a scan line that is optically associated with that photodetector. A photodetector response is transduced into a data signal (usually a voltage signal) whose intensity is proportional to the intensity of the light that the photodetector experiences during an interval of time called a “sampling interval”. A plurality of such data signals from the array of photodetectors is then processed by data processing systems well known to the electrophotography scanning arts.